Development of cattle TB vaccines based on heterologous prime-boosting strategies

AbstractDevelopment of a TB vaccine for cattle is a research priority in Great Britain. Two challenges need to be addressed. Firstly, vaccine strategies enhancing the efficacy of M. bovis bacille Calmette Guérin (BCG), currently the only potentially available TB vaccine, and secondly the development of a diagnostic test to be used alongside vaccination to differentiate vaccinated and infected animals (DIVA test). Significant progress in developing TB vaccines for cattle has been made over the last 7 years. Specifically: (i) DNA, protein, or viral subunit subunit vaccines used in combination with BCG have been shown to give superior protection against experimental challenge in cattle than BCG (heterologous prime-boost), (ii) neonatal BCG vaccination provides protection, (iii) prototype reagents that allow discrimination between vaccinated and infected animals have been developed; and (iv) and correlates of disease severity have been identified that can predict the success or failure of vaccination. The present overview provides details of some of these advances. [Ethiop.J.Health Dev. 2008;22(Special Issue):100-104

CD4+ and πσT Cells are the main Producers of IL-22 and IL-17A in Lymphocytes from Mycobacterium bovis-infected Cattle

Gene transcription studies have identified dual roles for the cytokines IL-17A and IL-22 in bovine tuberculosis, where they show potential as both predictors of vaccine success and correlates of infection. To allow for a detailed investigation of the cell populations responsible for production of these cytokines, we have utilised a novel bovine IL-22 specific recombinant antibody for flow cytometry. Bovine tuberculin (PPDB) induced greater IL-22 and IL-17A production in Mycobacterium bovis (M. bovis)-infected cattle compared to non-infected controls, while PWM-induced cytokine levels were similar between the two groups. In M. bovis-infected animals, PPDB specific IL-22 and IL-17A responses were observed in both CD4+ T cell and γδ T cell populations. Although both cytokines were detected in both cell types, IL-22/IL-17A double producers were rare and confined mainly to the γδ T cell population. These results support previous gene transcription studies and extend the observation of increased IL-22 and IL-17A responses in M. bovis-infected animals to the level of protein production. We were also able to characterise the cell populations responsible for these disease-related cytokine responses. The data generated can be used to further our understanding of the immunopathology of bovine tuberculosis and to produce more sensitive and specific immune-diagnostic reagents

T-Cell and Antibody Responses to Mycobacterial Antigens in Tuberculin Skin-Test-Positive Bos indicus and Bos taurus Cattle in Ethiopia

Higher IFN-γ responses to mycobacterial antigens were observed in Bos taurus (Holsteins) than in Bos indicus (Zebu) cattle which could due to differences in antigen recognition profiles between the two breeds. The present study was conducted to evaluate mycobacterial antigen recognition profiles of the two breeds. Twenty-three mycobacterial antigens were tested on 46 skin test positive (24 Zebu and 22 Holstein) using enzyme-linked immunospot assay (ELISPOT) and multiple antigen print immunoassay (MAPIA). Herds from which the study cattle obtained were tested for Fasciola antibody. The T cells from both breeds recognized most of the mycobacterial antigens at lower and comparable frequencies. However, antigens such as CFP-10, ESAT-6, Rv0287, Rv0288, MPB87, Acr-2, Rv3616c, and Rv3879c were recognized at higher frequencies in zebu while higher frequencies of T cell responses were observed to Hsp65 in both breeds. Furthermore, comparable antibody responses were observed in both breeds; MPB83 being the sero-dominant antigen in both breeds. The prevalence of Fasciola antibody was 81% and similar in both breeds. This piece of work could not lead to a definitive conclusion if there are differences in mycobacterial recognition profiles between the two breeds warranting for further similar studies using sound sample size from the two breeds

The humoral immune response to BCG vaccination

Bacillus Calmette Guérin (BCG) is the only currently available vaccine against tuberculosis (TB), but it confers incomplete and variable protection against pulmonary TB in humans and bovine TB (bTB) in cattle. Insights into the immune response induced by BCG offer an underexploited opportunity to gain knowledge that may inform the design of a more efficacious vaccine, which is urgently needed to control these major global epidemics. Humoral immunity in TB and bTB has been neglected, but recent studies supporting a role for antibodies in protection against TB has driven a growing interest in determining their relevance to vaccine development. In this manuscript we review what is known about the humoral immune response to BCG vaccination and re-vaccination across species, including evidence for the induction of specific B cells and antibodies; and how these may relate to protection from TB or bTB. We discuss potential explanations for often conflicting findings and consider how factors such as BCG strain, manufacturing methodology and route of administration influence the humoral response. As novel vaccination strategies include BCG prime-boost regimens, the literature regarding off-target immunomodulatory effects of BCG vaccination on non-specific humoral immunity is also reviewed. Overall, reported outcomes to date are inconsistent, but indicate that humoral responses are heterogeneous and may play different roles in different species, populations, or individual hosts. Further study is warranted to determine whether a new TB vaccine could benefit from the targeting of humoral as well as cell-mediated immunity

A mycobacterial growth inhibition assay (MGIA) for bovine TB vaccine development

Human tuberculosis remains a significant cause of mortality and morbidity throughout the world. The global economic impact of bovine TB is considerable. An effective vaccine would be the most cost-effective way to control both epidemics, particularly in emerging economies. TB vaccine research would benefit from the identification of an immune correlate of protection with which vaccines could be gated at both preclinical and clinical levels. In-vitro mycobacterial growth inhibition assays (MGIA) are functional assays that include most aspects of the complex host immune response to mycobacteria, and they may serve as functional immune correlates for vaccine development. We applied to cattle an MGIA that was developed for use with human and murine samples. Several technical difficulties were encountered while transferring it to the cattle model. However, our data demonstrate that the assay was not discriminatory in cattle and further work is needed before using it for bovine TB vaccine development

The intractable challenge of evaluating cattle vaccination as a control for bovine tuberculosis

Vaccination of cattle against bovine Tuberculosis (bTB) has been a long-term policy objective for countries where disease continues to persist despite costly test-and-slaughter programs. The potential use of vaccination within the European Union has been linked to a need for field evaluation of any prospective vaccine and the impact of vaccination on the rate of transmission of bTB. We calculate that estimation of the direct protection of BCG could be achieved with 100 herds, but over 500 herds would be necessary to demonstrate an economic benefit for farmers whose costs are dominated by testing and associated herd restrictions. However, the low and variable attack rate in GB herds means field trials are unlikely to be able to discern any impact of vaccination on transmission. In contrast, experimental natural transmission studies could provide robust evaluation of both the efficacy and mode of action of vaccination using as few as 200 animals

A comparative study on the epidemiology and immuno-pathology of bovine tuberculosis in Bos indicus and Bos taurus cattle in Ethiopia

AbstractBovine tuberculosis is a disease of dual effect, having public health and economic implications. The present study was conducted on its epidemiology and immuno-pathology in Holstein and Zebu breeds of cattle. Skin test, post mortem examination and pathology scoring, bacteriology, whole blood gamma interferon assay, ELISPOT assay, and lateral flow assay were used. An overall prevalence of 13.5% (n=5,424) was recorded; both prevalence (2 =61.8; P<0.001) and severity of pathology (mean pathology scores + SEM: 6.84±0.79 vs. 5.21±0.30; P=0.018, Mann-Whitney test) were significantly higher in Holstein than in Zebu. Similarly, IFN- responses to avian PPD (0.490.10 vs. 0.390.07), bovine PPD (0.630.11 vs. 0.430.07), or the ESAT6-CFP10 protein cocktail (0.430.01 vs. 0.300.05) were significantly higher (for all antigens: p<0.02) in Holstein than in Zebu cattle. However, both Holstein and Zebu exhibited similar T cell and antibody responses to different mycobacterial antigens i.e. no repertoire difference was observed between the two breeds. Thus, the present study showed increased susceptibility of Holsteins to bovine TB as compared to Zebu, similarity between Holsteins and Zebus in their antigen responses, and a positive correlation between IFN- responses and severity of pathology of bovine TB. [Ethiop.J.Health Dev. 2008;22(Special Issue):132-134

Characterization of effector and memory T cell subsets in the immune response to bovine tuberculosis in cattle

Cultured IFN-γ ELISPOT assays are primarily a measure of central memory T cell (Tcm) responses with humans; however, this important subset of lymphocytes is poorly characterized in cattle. Vaccine-elicited cultured IFN-γ ELISPOT responses correlate with protection against bovine tuberculosis in cattle. However, whether this assay measures cattle Tcm responses or not is uncertain. The objective of the present study was to characterize the relative contribution of Tcm (CCR7+, CD62Lhi, CD45RO+), T effector memory (Tem, defined as: CCR7-, CD62Llow/int, CD45RO+), and T effector cells (CCR7-, CD62L-/low, CD45RO-), in the immune response to Mycobacterium bovis. Peripheral blood mononuclear cells (PBMC) from infected cattle were stimulated with a cocktail of M. bovis purified protein derivative, rTb10.4 and rAg85A for 13 days with periodic addition of fresh media and rIL-2. On day 13, cultured PBMC were re-stimulated with medium alone, rESAT-6:CFP10 or PPDb with fresh autologous adherent cells for antigen presentation. Cultured cells (13 days) or fresh PBMCs (ex vivo response) from the same calves were analyzed for IFN-γ production, proliferation, and CD4, CD45RO, CD62L, CD44, and CCR7 expression via flow cytometry after overnight stimulation. In response to mycobacterial antigens, ~75% of CD4+ IFN-γ+ cells in long-term cultures expressed a Tcm phenotype while less than 10% of the ex vivo response consisted of Tcm cells. Upon re-exposure to antigen, long-term cultured cells were highly proliferative, a distinctive characteristic of Tcm, and the predominant phenotype within the long-term cultures switched from Tcm to Tem. These findings suggest that proliferative responses of Tcm cells to some extent occurs simultaneously with reversion to effector phenotypes (mostly Tem). The present study characterizes Tcm cells of cattle and their participation in the response to M. bovis infection